Arc discharge tubes or switches



Oct. 16, 1962 L. v. MCCARTY ElAL 3,059,136

ARC DISCHARGE TUBES QR SWITCHES 2 Sheets-Sheet 1 Filed Nov. 8, 1960 INVENTORS Lo'uabes V Mc CARTY BAYARD H. M\CHAEL.

A-r-roauav Oct. 16, 1962 L v. MOCARTY EIAL 3,059,136

ARC DISCHARGE TUBES 0R SWITCHES 2 Sheets-Sheet 2 Filed Nov. 8. 1960 4. 414 vllitvailllllllifillllllill rlll1l lllllllilfilvli :I A 5 in 4! v jimszvrok. Louaoes V. McCABJfH. 'BAYARD H. Mucufifl.

- 3,059,136 ARC DISCHARGE TUBES R SWITCIES Lourdes V. McCarty and Bayard H. Michael, Milwaukee, Wis, assignors to Controls Company of America, Schiller Park, 11]., a corporation of Delaware Filed Nov. 8, 1969, Ser. No. 68,048 Claims. (Cl. 313-165) This invention relates to are discharge tubes or switches of the type having a mercury pool cathode which is ignited to ionize the mercury and permit current flow between the cathode and anode. In such tubes there is a migration of mercury to the anode and there must be provision for return of this mercury to the cathode. Tube designs in the art have either not made adequate provision for this return with resulting improper tube performance or have resorted to costly tube structures to effect the return. The tube must also make provision for cooling lest the heat of the tube vaporize the mercury and cause misfire of the tube.

The principal object of this invention is to provide a lower cost tube making provision for condensate return and adequate cooling.

This object has been attained in application to a tube of the type having a capacitative igniter and it is another object of this invention to improve such igniters. The solution results in the igniter becoming part of the condensate return (although the condensate return is quite practical when applied to tubes having other igniter arrangements).

Other objects and advantages will be pointed out in, or be apparent from, the specification and claims, as will obvious modifications of the two embodiments shown in the drawings, in which:

FIG. 1 is a cross-section of one form of tube; and

FIG. 2 is a cross-section of another tube.

Referring to FIG. 1 in detail, the tube has a glass body 10 generally in the nature of an inverted J. The lower end of the shorter leg of the tube is provided with a metal cap 12, such as Kovar, which is sealed to the glass and has a depending flange 14 to which the glass tube 16 is sealed. A glass dam or weir 18 is fixed above the central opening of the metal cap so as to provide an annular pool containing mercury 20. The mercury pool will have a level substantially shown in the drawing and any excess mercury tending to collect here will overflow weir 18 and run down tube 16. This pool is the anode pool of the tube and an electrode 22 is connected to the Kovar cap. The are cannot touch the Kovar at any time and, hence, the Kovar is not subjected to any wear due to electron bombardment.

The mercury running down the return tube 16 will seek a level 24 as shown in the drawing, this comprising one leg of what amounts to a U tube. The mercury level 24 stands above the Kovar fitting 26 connecting the tube 16 to the Kovar or metal tube 28. It will be seen that all the metal parts here are protected by mercury. The tube 28 is provided with another fitting 30 at its right-hand end to connect the small bore tube to the glass cylinder 32 which has a central bore 34 leading about half-way through the cathode pool 36. The upper end of the glass cylinder 32 is connected to the metal cap 34, which in turn is sealed to the bottom end of the long leg of the tube. At the top of the tubular extension of the cylinder 32 there is sealed an artificial sapphire stand pipe or igniter 38. The mercury will rise inside the central bore of the sapphire igniter and form a meniscus 40, the top of which will be level with the level 24 on the other side of the condensate return path. As mercury falls from the anode pool, it will, of course, force mercury out of the igniter and this will fall from the curved upper lip of the igniter to the cathode pool. By providing the curved 3,fi59,l3 Patented Get. 16, 1952 upper lip, the mercury cannot run down the side of the igniter to, in effect, short circuit the igniter. Thus, even though the upper end of the igniter is open and filled With mercury, the igniter remains of the capacitive type. One lead 42 from the high voltage side of the firing transformer 44 is connected to the Kovar tube while the other lead is connected to the cap 34. Thus, when the firing circuit, connected to the low voltage leads to the firing transformer, is energized a potential will be set up between the mercury inside the igniter 38 and the cathode pool, and this potential will ionize some mercury to permit an arc discharge between the cathode and anode through the ionized path.

It will now be seen that the condensate return path from the anode is external of the tube and hence, can be fully cooled as well as permitting the tube to be cooled. This tube arrangement of an inverted J permits superior cooling of the anode itself. In fact, the entire tube can now be immersed in a suitable coolant which can of course be circulated. The present igniter structure is both simple and effective and has now become part of a condensate return path and with the curved, over-hanging lip is so arranged that the mercury flowing from the center of the igniter cannot run down the outside of the igniter to short circuit the firing. A final advantage of this is that since the igniter is open, there is no problem of expansion within a closed igniter. The use of the mercury within the igniter insures intimate contact with the dielectric of the igniter.

It will, of course, be appreciated that the tube is evacuated as may be done, for example, through the pinched oil tubular portion 46 at the upper end of the tube. The tube structure illustrated here can be subjected to reverse potential to blow out the are at any time rather than requiring the current to decay to zero after ignition.

In FIG. 2 the Kovar condensate return tube 28 is connected to the Kovar cap 50 so the condensate is returned directly to the cathode pool 36. This arrangement utilizes a more conventional igniter comprising the closed artificial sapphire sheath 52 sealed to glass seal 54 through which electrode 56 passes to make electrical connection with the mercury 58 inside the sheath. The level of the igniter mercury 58 is above the level of the cathode pool. The operation of this tube is much the same as the tube in FIG. 1 with one lead 42 from transformer 44 being connected to return tube 28 and the other lead being connected to the igniter electrode.

This second embodiment retains the superior cooling attributes of the first embodiment while using more conventional igniter arrangement or such other igniter arrangement as may be thought desirable.

Although but two embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein Without departing from the spirit of the invention or from the scope of the appended claims.

We claim:

1. A mercury arc discharge tube comprising, an evacuated tube, a mercury cathode pool, a mercury anode pool, an igniter for the cathode, and a separate confined flow path for mercury to flow from the anode to the cathode, said flow path being defined by a conduit which projects through the anode pool to the surface thereof.

2. A tube according to claim 1 in which the conduit runs outside the tube between the pools.

3. A tube according to claim 2 in which the cathode end of the conduit terminates inside the igniter, the igniter projecting above the cathode pool and being open ended so overflow can run from the igniter to the cathode pool.

4. A tube according to claim 3 in which the open end of the igniter is flared.

. r a r 3 t 5. A mercury arc discharge tube comprising, an evacuated tube containing an anode and a mercury poolcathode, an open ended dielectric igniter sheath extending up through the cathode p001 and containing mercury at a level above the pool, and 'means for replenishing the mercury in the pool. a

6. A tube according to claim 5 in which the means includes means for collecting mercury condensate from the anode and leading it to the interior of the sheath. 7. A tube according to claim 6 in which the replenishing means includes a conduit external of the tube.

8. A tube according to claim 7 in which the anode is a mercury pool and is positioned in intimate contact with the outside of the tube to permit cooling of the anode.

9. A mercury arc discharge tube comprising, an evacuated tube in the general shape of an inverted J, a mercury pool cathode at the bottom of the long leg of the J, a mercury pool anode at the bottom of the short leg of the J whereby the anode is elevated with respect to the cathode, an igniter for the cathode pool, and a conduit external of the tube for returning to the cathode pool mercury which condenses at theanode in operation of the tube said mercury returned to the cathode being that in excess of a given level in the anode pool, said conduit returning the mercury to the cathode pool via the interior of the igniter, whereby the level in the igniter is above the level in the cathode pool.

10. A tube according to claim 9 in which the igniter is open above the level in the cathode pool and the opening is flared to prevent returning mercury from running down the side of the igniter.

References Cited in the file of this patent UNITED STATES PATENTS 1,402,931 Hewitt Jan. 10, 1922 

